This application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2007-033847 filed in Japan on Feb. 14, 2007, the entire contents of which are herein incorporated by reference.
The present invention relates to image forming apparatuses such as copiers, printers, and facsimile machines, and particularly relates to paper transport paths of image forming apparatuses in which a recording paper is temporarily stopped by registration rollers then transported to a print processing portion.
With this type of image forming apparatus, development has been advancing in recent years toward apparatuses having increased print processing speeds, for example apparatuses have been developed that perform print processing on 100 or more sheets/min. In this regard, along with increased print processing speeds such as these, much greater loads are being placed on paper transport mechanisms.
For example, when carrying out print processing at 100 sheets/min, it is necessary to set the print processing speed to approximately 450 to 600 mm/sec. On the other hand, to ensure an adjustment time in which the recording paper is temporarily stopped by the registration rollers immediately before the step of print processing, it is necessary to set the transport speed of the recording paper on the upstream side from the registration rollers at 600 to 1,500 mm/sec, which is even faster than the print processing speed, so as to make faster the timing by which the recording paper reaches the registration rollers, thereby gaining time for the adjustment there. This adjustment time is set so that the leading edge of the recording paper is aligned parallel to the registration rollers and also so that a timing by which the leading edge of the recording paper reaches the print processing step and a timing by which print processing commences are caused to coincide. In other words, along with increased print processing speeds, there is a necessity to set the transport speed of the recording paper on the upstream side from the registration rollers even faster, and this is a cause of placing much greater loads on paper transport mechanisms.
Furthermore, since it is difficult to achieve high-speed print processing with only higher transport speeds of the recording paper, the distance of the spacing between a preceding recording paper and a succeeding recording paper is being made smaller (see JP 2005-247267A).
However, the distances of spacing between recording papers is not always held constant and may vary. For example, recording paper is picked up and fed by a pickup roller in a paper feed portion, but due to variation in the extent of slipperiness of the surface of the recording paper, the pickup roller may slip such that the timing by which the recording paper is picked up may be delayed, thereby increasing the distances of spacing between the recording papers. Furthermore, when a preceding recording paper is picked up by the pickup roller, if the succeeding recording paper thereunder is dragged up by the preceding recording paper, then the succeeding recording paper will not return to its original position even if the succeeding recording paper is pulled apart from the preceding recording paper by separator rollers, and therefore the succeeding recording paper is picked up in a state in which it is close to the preceding recording paper, thereby reducing the distance of spacing between the recording papers.
For this reason, in a case where the distance of spacing between recording papers is set smaller in order to increase the speed of print processing as in JP 2005-247267A, the distance of spacing between recording papers is made even smaller when the succeeding recording paper is pulled up by the preceding recording paper, and there are large shifts in the timings by which the succeeding recording papers reach the registration rollers, such that transport control of the recording paper by the registration rollers is made difficult.
For example, in a case where the distance of spacing is set to 50 mm, when the succeeding recording paper is dragged up by the preceding recording paper by 30 mm, then the succeeding recording paper after that is picked up 30 mm earlier, and therefore the distance of spacing between the recording papers becomes 20 mm such that the timing by which the succeeding recording paper reaches the registration rollers is greatly shifted.
Accordingly, the present invention has been devised in consideration of the conventional problems, and it is an object thereof to provide a paper transport path of an image forming apparatus capable of adjusting the distance of spacing between recording papers when successively transporting a plurality of recording papers.